La Crosse Virus Infection Research Articles

Rapid diagnosis of LaCrosse encephalitis: detection of specific immunoglobulin M in cerebrospinal fluid.

An immunoglobulin M (IgM) antibody capture enzyme immunoassay (MAC-EIA) was developed for the rapid and early diagnosis of LaCrosse (LAC) virus infections. The MAC-EIA was a sensitive and specific technique for the detection of IgM antibodies to LAC virus in cerebrospinal fluid specimens and in acute-phase serum specimens. In a retrospective study, cerebrospinal fluid and acute-phase serum paired samples from 108 patients were tested by the MAC-EIA and by an IgM immunofluorescence assay. The results were compared with the original diagnosis, which was made by using a variety of classical serological tests including serum neutralization, hemagglutination inhibition, and complement fixation. Thirty patients were confirmed as having LAC virus infections; of these, 30 (100%) were diagnosed as positive by serum MAC-EIA, and 27 (90%) were positive by cerebrospinal fluid MAC-EIA. The MAC-EIA was more sensitive than the IgM immunofluorescence assay. Two patients who were not previously confirmed as positive cases were diagnosed as having LAC virus infections by the MAC-EIA. One patient who was subsequently diagnosed as having a Jamestown Canyon virus infection and two patients who were previously infected with Jamestown Canyon virus were not falsely identified as having LAC virus infections by the MAC-EIA.

Experimental La Crosse virus infection of red fox (Vulpes fulva), raccoon (Procyon lotor), opossum (Didelphis virginiana), and woodchuck (Marmota monax).

Susceptibility to infection, resulting viremia and antibody responses, and potential to provide infectious blood meals for Aedes triseriatus were determined and compared for the red fox (Vulpes fulva), raccoon (Procyon lotor), and opossum (Didelphis virginiana) exposed to La Crosse (LAC) virus transmitted by mosquitoes, Ae. triseriatus. Woodchucks (Marmota monax) were infected with LAC virus by needle and syringe. All 5 red foxes became viremic following the bite of a single LAC virus-infected female Ae. triseriatus. Maximum viremia titers were at or above the threshold of infection for Ae. triseriatus in 4 of 5 red foxes for 1-3 days. Biological transmission of LAC virus from infected red foxes to chipmunks (Tamias striatus) was accomplished by Ae. triseriatus. Neutralizing antibody titers in red foxes peaked between day 13 and 27 and were still detectable 3 months post-infection. Woodchucks appear to be efficient amplifiers of LAC virus. Three of 4 inoculated woodchucks became viremic. Maximum viremia titers were consistently above the experimentally determined threshold of infection for Ae. triseriatus. Raccoons and opossums were not as susceptible to LAC virus infection as were red foxes or woodchucks. Only 1 of 5 raccoons became viremic. The viremia titer was low and was detected on only 1 day. Four of 5 raccoons developed LAC virus-neutralizing antibody titers, however. None of the opossums became viremic and only 2 developed LAC virus-neutralizing antibody titers.

Evaluation of Immunofluorescence and Cell Culture Techniques for Detecting La Crosse Virus Infection in Individual Aedes Triseriatus (Diptera: Culicidae)1

Two methods, (1) the indirect immunofluorescent antibody technique (IFAT) using head squashes, and (2) the method of tissue trituration and inoculation of supernatant into a susceptible assay system, were evaluated for detection of La Crosse (LAC) virus infection of individual Aedes triseriatus . Twenty-one days after fully engorging on an infectious blood meal containing LAC virus, 63% (119/189) of the control group females transmitted virus to suckling mice; virus infection persisted in 97% (184/189) of the control group females. The test group females were cut into 3 parts (head, anterior thorax, abdomen) to determine the extent of viral infection using IFAT on head squashes and the trituration method on thoracic and abdominal tissues. Head-squash I FAT indicated 71% (52/73) of the test group had disseminated infections; 21% (15/73) had nondisseminated infections. Exclusive use of head-squash IFAT would have indicated a 3 to 24% lower infection rate than the trituration method. However, judicious use of the IFAT will save time and reduce the cost of assay, since only mosquitoes with negative head squashes need be further assayed; in this study a 70% reduction in individual trituration assays would have been realized. A comparison of test and control groups indicated disseminated infections could not be directly equated with the probability of virus transmission.

Capture immunoglobulin M system for rapid diagnosis of La Crosse (California encephalitis) virus infections.

A capture immunoglobulin M (IgM) enzyme immunoassay was developed to diagnose La Crosse virus infections by the detection of specific IgM in acutephase serum specimens. IgM was detected by the capture IgM system in the serum of 24 of 29 (83%) of the patients studied. In comparison, IgM was detected in 19 of 29 (66%) of the patients by an indirect immunofluorescence technique. Specific IgM was detected in 83% (20 of 24) of patient serum specimens by day 3 after the onset of clinical symptoms.

La Crosse virus infection and disease in western North Carolina.

Active surveillance for La Crosse infection from 1977 to 1979 revealed 12 laboratory documented cases in children from the Cherokee reservation and nearby areas of western North Carolina. The annual rate of hospitalization with La Crosse virus was isolated from two of 34 pools of male and one of 34 pools of female Aedes triseriatus mosquitoes reared from larvae collected around the residences of reservation children who had been hospitalized with encephalitis. The occurrence of the recent cases, the history of cases in 1964 and 1965, and the demonstration of antibodies to La Crosse virus in sera from second grade children collected in 1968 (2%), in 1978 (4.5%), and in high school students in 1979 (11.3%), indicate that La Crosse has persisted in the Cherokee area for at least 15 years. La Crosse infection is infrequently reported from the southeast, but this may reflect inactive surveillance. More frequent testing would reveal whether La Crosse is a significant health problem in other areas of the southeast.

Indirect fluorescent-antibody technique for serological diagnosis of La Crosse (California) virus infections.

A clinically relevant indirect fluorescent-antibody technique (IFA) was developed for the serological diagnosis of La Crosse virus infections. The IFA (67%) was as sensitive as the hemagglutination inhibition (58%) and neutralization (58%) tests in the detection of antibodies in acute-phase specimens. Immunoglobulin M antibodies were detected by the IFA test in 48% (11 of 23) of these specimens. Diagnostically significant increases in IFA titer were detected in 86% (19 of 22) of the paired samples. Antibodies were detectable in some patients 7 years after infection; however, the IFA test was not as sensitive as the other two tests in the detection of previous infections.

Natural La Crosse Virus Infection in the Red Fox (Vulpes Fulva), Gray Fox (Urocyon Cinereoargenteus), Raccoon (Procyon Lotor), and Opossum (Didelphis Virginiana) *

Natural infection of sentinel red foxes (Vulpes fulva) and free-ranging red foxes, gray foxes (Urocyon cinereoargenteus) and raccoons (Procyon lotor) with La Crosse (LAC) virus was demonstrated. One isolate of LAC virus was obtained from a sentinel red fox in an enzootic area. The viremia titer of the LAC virus-infected red fox was above the threshold of infection for Aedes triseriatus mosquitoes. Antibody responses were measured by the microneutralization test employing four California group viruses: LAC, snowshoe hare, trivittatus, and Jamestown Canyon. Four of six sentinel red foxes developed LAC virus neutralizing antibody. Antibody titers peaked between days 7 and 34 and were still detectable by dat 345 post-infection. Homologous LAC virus antibody titers were consistently 4-fold or greater than heterologous titers. Serological evidence for natural LAC virus infection was demonstrated in 33 of 57 (58%) free-ranging red foxes, 18 of 32 (57%) gray foxes, and 4 of 16 (25%) raccoons. Antibody titers were comparable in free-ranging foxes infected naturally and those infected experimentally by mosquito bite. The prevalence of infection was significantly different (P less than 0.001) for foxes trapped on three distinct areas within the enzootic region. Rates of infection in foxes by area coincided with LAC virus antibody prevalence observed in free-ranging chipmunks and with reported cases of human LAC encephalitis in Wisconsin.

Infection rates of Ascocystis-infected Aedes triseriatus following ingestion of La Crosse virus by the larvae.

The La Crosse (LAC) virus infection rate of Aedes triseriatus larvae that ingest LAC virus does not appear to be increased by concomitant infection of larvae by the gregarine parasite, Ascocystis barretti. Infection rates ranged only from 0--2.6% in adult Ae. triseriatus reared from groups of A. barretti-infected larvae that had ingested LAC virus (California encephalitis group) at dosages of 2.0--7.7 log10 SMICLD50/ml. Females resulting from orally infected larvae transmitted LAC virus to suckling mice. Larvae that were infected with A. barretti and devoured carcasses of adult mosquitoes containing 4.7 log10 SMICLD50/ml failed to become infected. A. barretti spores developing in transovarially infected mosquitoes did not harbor LAC virus; thus, A. barretti does not appear to be a mechanism for virus dispersal.

Diagnosis of California La Crosse virus infection by counterimmunoelectrophoresis.

La Crosse virus cell culture-derived soluble antigen was used in a counterimmunoelectrophoresis procedure to assess the presence or absence of La Crosse antibodies in 79 paired acute- and convalescent-phase human sera. The counterimmunoelectrophoresis test appeared to measure the same antibody as the complement fixation test but was more sensitive and rapid.